1. Field of the Invention:
This invention relates in general to equipment for drilling subsea wells from a floating vessel, and in particular to a running tool for use in drilling the initial portions of the well.
2. Description of the Prior Art:
In drilling a well in deep water, a floating vessel will be used. A template or guide base will be located on the subsea floor. When starting the well, large diameter conductor pipe, normally 30 inches in diameter, is lowered from the vessel and through a well receptacle in the template. Drill pipe extends through the conductor pipe. A drilling tool such as a drill bit and a drill mud motor will be located at the bottom of the conductor pipe. A wellhead housing is located at the upper end of the conductor pipe string. A running tool locates in the wellhead housing and supports the drill bit at the bottom of the conductor pipe.
Drilling fluid is pumped down the drill string to cause the mud motor to rotate the drill bit to drill the hole for the conductor pipe. Alternately the hole is drilled by jetting alone, without using a mud motor. As the hole deepens, the conductor pipe is lowered into the well. When at the desired depth in the well, typically about 300 feet, the wellhead housing will be located at the template. The running tool and drill bit are removed from the well. The running tool is removed from the drill string.
Then, the drill string is again lowered through the conductor pipe and used to drill the second portion of the well. This second portion is drilled to a depth of about 1,000 feet. After this portion is drilled, the drill string is pulled, and a string of casing is lowered through the conductor pipe and cemented in place. Drilling will then continue.
While this is successful, removing the drill bit from the conductor pipe, taking off the running tool, and lowering the drill bit back in to drill the second portion of the well is time consuming in deep water.
One type of running tool is used which enables the operator to drill the second portion of the well without retrieving the running tool and drill bit to the surface. That running tool has double J-slots. One J-slot secures the running tool in the wellhead housing. Another J-slot releases the drill string from the running tool to allow it to drill ahead. While workable, actuating two J-slots can be difficult with a floating vessel because of the wave action.